is the 1515L just a louder 115L or does it produced a little deeper lows? could someone explain to me too what the difference in sound would be from the non-tweeter and tweeter versions?
The 115L is a very traditional, front ported, single speaker + tweeter box. It is quite 'tightly voiced' due to that big driver in a small box, and also due, I assume, to the voicing of the Celestion Neo driver. However, it is very even and smooth from the bass to the treble... no significant holes or peaks.
I have not heard the 1515L, but one thing that makes it very different is that it does not have a tweeter (there is a bigger 1515L+ that is two way. Also, from my experience with the 1212L+, a similar design (but with tweeter), having those two speakers crammed in a very little box, with one in an angled baffle, results in HUGE volume, tight, punchy tone, and unfortunately to my ear (at least with the 1212) a strong bump in the lower mids, and a dip in the upper mids. That can work very well in a mix (punchy, tight, loud) but can sound a little uneven solo.
I again really dig the super small size and low weight of the 115L+, and the even, tight sound. I was never a fan of a very small cab that was tuned very low. Those types of cabs sound great solo, but get quickly buried in a mix.
The 115L+ is the best balance of even tone, decent usable low end, and high SPL/loud volume in a small cab that I've experienced. I literally do full pop gigs with this thing and a small 500 watt amp (in my case, I use an LMII).
Wonderful cab.... 75% of the volume of the 1212L, with none of the peaks and valleys to my ear NOTE: I have NOT heard the new 1212L+ with the celestions... Jorg says it's a bit smoother in response).