There is a lot of training information out there about how to get faster riding hills. I usually tell people at first just ride more hills, but it sounds like you have done that and that you have made some headway in your hillclimbing. Don't ever denigrate that increases in your abilities. Just because you are not as fast as others does not mean that you have not improved! Celebrate those milestones and then try for more.
What most of us will do on hills is climb at a speed that we can sustain to the top. That may be slower for a long hill and faster for a short hill. Try some specific hill intervals to try to get faster overall on hill climbing. Find a hill that takes 8-10 minutes to get to the top. If that is too long to sustain at first, try 5 minutes. If you can't find a hill that long, just go up a hill for five minutes/8/10 minutes and then turn around and go back to the bottom. Go as hard as you can without blowing up. If you can't go any farther and get real slow, stop turn around and try again. Make sure that you are totally recovered at the bottom of the hill. If you have to stop or ride easy on teh flat at the bottom do so until your breathing and heartrate are under control again. Go hard again. Try 2 intervals the first week, twice a week. Try 3 intervals the second week, twice a week. Try 4 intervals the third week, twice a week. Take a break the fourth week. The next month do 3 intervals the 1st week, x2; 4 the second week, 4 the third week and take a break. After two months of this, see if you aren't faster overall on the hills.
Remember - you will be faster - maybe not as fast as you want but patience, speed comes with dedication, training and time! But always remember don't get discouraged - YOU ARE GETTING BETTER!