I'm 15 years old, and my range is A5-B1. Is there any chance that my range will get any lower? I really enjoy singing bass and wish I could sing a G1.
Oh definitely, with consistent practice and breath training you can get lower and higher. Just stretch your range at a natural pace (you can do exercises where you sing your lowest note and work up to the highest and back down).
At age 15, your voice might still have some room to grow deeper as your physiology matures. The larynx and vocal chord tissue does not fully mature in many males until late teens.
But even if your voice is fully developed from a physiological perspective, there are exercises and practice techniques that can help you improve the quality of your voice and expand your range to some extent.
I would encourage you to consider hiring a vocal coach or taking voice lessons from a qualified teacher. A professional can evaluate your technique and current capabilities and prescribe specific exercises and practice drills designed to improve the overall quality of your singing and expand your range.
The sooner you begin intention exercises and establish a proper and appropriate practice regimen, the better your results will be. Good luck!
A B1 will not be a limitation for singing bass. That's already in the contra octave, below basso profundo range. If you want to become a bass, you should focus your efforts on getting better instead of lower! A5 is high baritone range, so also not an issue.
Range is a one-dimensional quality. If you can maintain what you claim you have, you've got it covered. But there is a whole lot more to singing than just range.