would a vox ac15 be ok to gig with?

Yes, I use a little 15 watt Fender Blonde Blues Jr. most of the time ...mainly because I got tired of dragging around a 65lb Twin Reverb.

Some will tell you to use a bigger amp, but if you play larger gigs, consider mikeing your amp through the PA (SM 57 microphone) or if the Vox has a "line out," you can run a cable from that output into the PA.

Test this line out first, because some VOX amps will cut all volume from the main speaker...and I've never liked that feature....you want to be able to hear your amp on stage. If your amp does this, you will have to mike it.

Since it's a small amp, I also recommend an amp stand...they aren't too much these days...around $25.

Best of luck.

Yes, it would make a fantastic gigging amp. As Stan said, in a gigging scenario you'll likely be micing the amp and with the smaller tube amps this allows you to still drive your tubes into saturation without overpowering the microphone. This is a problem especially for those guys with 100 watt heads and the 4x12 half-stacks. They've either got the master volume pushed down to the point of almost no tube saturation, or they're overloading the mic (or they're at the story spending $300 on a Hot Plate attenuator). The only thing you're losing is the iconic image, but you gain a more practical stage setup. If you're not playing with a P.A. system, 15 tube watts should suffice if it's a small venue. Just tell the drummer to take it easy. :)