Dude, i would strongly suggest u get the cube 30 instead (sigh here we go again haha..) Reasons being:
1.) Bigger speaker. The difference in tone between 8" and 10" is audible. Even if u are not able to discern the difference now, when u really do, at least u will be glad u got the cube 30 and not spend additional cash upgrading.
Idea being: since both sound the same now, but if i know one is gonna sound better next time i become a pro guitarist, might as well take the better one.
2.) The range of drive sounds u get is much more compared to the cube 15. Cube 15 has only 4 drive sounds, each given just a generic name. Cube30 has 7, each emulating a particular amp sound. Each sound is distinctly different, giving u more tones to play with. And u can easily switch from acoustic to death metal with just a simple twist.
And this is good, cos u save the $$ from spending on a multi effects pedal next time (trust me, everyone will get to this phase lol). This in itself is like a multi effects pedal. Sometimes when im lazy i decide not to hook up all my effects just to get a jam going. Just plug into the cube30 and u are good to go!
The various effects tt come with the cube 30 give u a good preview of how these effects sound and how they interact with distortion bla bla. With the cube 15 u can't get to play with these effects, and when u do want to learn abt them nxt time u will be thinking of investing on a multi efx pedal, which in due time u will want to sell again. So might as well buy it once and for good.
Once again, it's good for lazy jam sessions where it's just u ur guitar and ur amp. And u have access to everything
Personally i feel that the cube series is a good investment in itself as the recording function of it is pretty useful. Low noise and the drive channels are decent enuff to be used for recording. Like hifi_killer asked me once,
"is that a tubescreamer?"
"no it's just the tweed channel on the cube 30"
i love my cube.