There is more than 15W available from these amps if you're talking about higher THD and you stay away from low frequency content.
Anecdotally I know tons of people using 87dB sensitive speakers on 2-4W amps who are quite happy with the output level from their systems.
I have a pair of Clearfield Continentals by Counterpoint that are 87db 4 ohms. I can tell you, it depends on the room size and person's use to how loud any 87db or lower speaker will play.
I was surpised when I finally put my Latino VTA-120 power amp with tube rectifier into my system and sound way better/bigger. I was actually shocked how well the VTA-120 pushed them and when I push them really hard the VTA-120 didn't even stress! I did have a Old School Mullard GZ37 rectifier installed as well when I was playing them like that. I don't know if this made any diffrence but I was happy it didn't blow the rectifier like it did with a new JJ GZ34 the first week after I built the VTA-120 and hardly turned it up. I did eventually go to a single and then a double subwoofers but never used a separate crossover for this. I just set the subs at around 40hz with the speakers running in full range. With that combo the system gets pretty loud in my room of 14'X20' with furniture.
The VTA-120 is rated @60watts but really did a great job at pushing the Clearfield Continental by Albert Von Schweikert. So I regularly plays these at loud levels since I built the amp about 5 years ago and have had zero issues with it. I do run the biasing @.50Vdc with Gold Lion KT88 tubes. The output transformers do get warm but nothing crazy or where I can't touch them.
I am too wondering about the weight of the Carver amp cause my VTA-120 has got to be close to or over 40lbs. The transformers were the most of the weight comes from when I was building it and they went on first. But, I would love to try the Crimson 275 out and see what it can do in "Real Life" situations and not just look at measurements.
I did see some where these will work best by using a subwoofer/s as I know this well with my own system. So maybe the best way to run these amps will be with subwoofers and crossed over around 70-90hz? From what I have read on many of the forums now all over the place about this amp, I always see they do sound really nice and even replaced bigger and more expensive gear.
like I said above, I was shocked at how well my VTA-120 pushed them Continentals without any stress in sound or soundstage, never felt they were running out of gas and felt they could give even more but didn't want to push it to a crazy level. They were loud enough that we were having to really talk loud getting close to shouting to comment on the system. But just dont know what the THD was/would be at these levels. Sounds good to me compared to my other amps with way better distortion (Edge M8, Classe CA-400, and Electrocompaniet AW250). Also Bob Latino did suggest using a SS rectifiers in the VTA-120 for louder playing levels.
The VTA-120 with my DIY 2way Horn speakers with Radian 475PB-8 CD's and MCM 2963 15" woofers doesn't need any help from subs and has pleanty of powerful clean tight bass that can shake the house and not even turned up very loud either.
I would love for someone from Carver to come here and give a detailed explaination about why the output transformers are so small other than what some brief literature has to say. From what has been confirmed so far by some other manufacturers they are Edcor custom output transformers but that's all that has been confirmed. I know they did mention it in their literature about the smaller lighter output transformers, so they never really hid that from anyone if they were reading the literature.
Also, when we are playing music and at good volume levels...isnt the power output still in the 15-25 watt range? I know more power can lead to better presentation but what most of us think is the system playing at 60-100watts at loud levels is actually at more like 15-25 watts with speakers with decent sensitivity in the 89-91db. range? I do get the 75 watt spec and why people are upset but hasnt there been things like that in other manufacturers output claims? Amps not meeting there output levels and then find again it measured at 1khz for that specific output but in real life never actually hit it?
Also with the Carver Crimson 275 amps, So the output tranformers wattage/size, wouldn't there have been some serious amp failures out in the field of use by now? I haven't seen anything in that regards.
Not here to argue, just to bring some questions from a different angle and share my experience with my tube amp with lower efficiency speakers.