Sans, I don't think you'll be happy with anything in the 15w range. Those little practice amps just suck all the way around. You wouldn't be any happier with it than your Ibanez. I have a Peavey Blazer 158 transtube (ss) that's the best I could find for a 15-watt starter amp.
I'm going to give you a good piece of advice here. How you choose to use it is entirely up to you.
Generally, I would say don't go under 25-watts for a practice amp. But when you buy one new, you'll be spending let's say $100- $120. For something that will be no better than your Ibanez.
I would say spend a little extra to get something that sounds decent.
I know, I KNOW, you hate ebay. But I found one of these on there just now:
http://xrl.us/be7zay
Dude the difference between one of those and any practice amp is astronomical! It puts ANY practice amp you'll find in a store to shame. Even if you ended up getting it for $150- $175. The difference is HUGE when it comes to the quality of the amp and sound!!
Not to mention, it would be a good backup to your Carvin. It's not as thick in the distortion. But it is 85 watts. More than enough for any small to medium sized venue without mic'ing.
85 watts, footswitch, Fender reverb. Awesome for recording. Great for practice. In a practice setting, you wouldn't even get the vol. knob past 2. You should be all over this amp! These little suckers blow away my Marshall MG-50 (which I paid $350 for) without even trying. And they're no bigger than a 25-watter.
These are the amps that HaleAmano regularly gigs with, and I promise you they sound great. To get one for under $200 is a good deal in my opinion. By the way, we'll be recording our cd with one of these.
Well, that would be my advice. If you don't have an ebay account, find someone who does and snag this gem. Rather than just looking for a practice amp, you could have 2 usable gigging amps as well as a practice amp.