My game uses multiple lights, shadows etc (see here) so the JME’s stock forward rendering is too slow in such situations.
Sometimes you need to do some work instead of replacing graphics card with better one. This is not an optimization, every time you need to take care about fps and performance. To be sure that even cheap home computers can run your game smoothly. You cannot write “buy better card” to any player with decent hardware. So it is very important to run every test on computer similar to your target platform.