Back to your original question of how to write faster than 15wpm.... Use the G4FON program and set the speed to 20/17 wpm as you with only 2 characters. Heck, just read the instructions with the program. This will teach you to write faster than 15 wpm. When I first passed my 13wpm general test, I could not really copy that fast, just a lucky day. I could just barely write 13wpm! Now I can sorta write 17wpm (working on 20 wpm) by the teaching/learning of the G4FON program.
I will move from 20/17 wpm to 20/15 wpm, and when first learning, even down to 20/12 wpm to learn the characters. BUT DO NOT add the next character until you can copy the 20/17 wpm session (at least 1 minute, better 2 minute) at better than 90%. I was able to copy 95% with 20/17 wpm until I got to 26 characters, then I just was progressing too slow. I finished the 41 characters at 20/15 wpm. Now after using it on the air some, I am going thru the sessions again and hoping to finish with 20/17 wpm. Heck, I can do some 2 minute runs with a full 20/20 wpm runs now (only 10 characters).
Realize, different folks learn differently. IF you happen to be musically inclined, you will learn languages AND code MUCH easier than us mere mortals.... BUT code can still be learned - just takes longer and more work.
Keep up the good work and hang in there!
73 de Ken H.
K9FV