HOA scared to raise condo fees, as some units are still not sold

Our HOA is only 24 units we are supposed to have 32. Because of economic times the other units have not been built. I moved in three years ago and assessment fees were $118.00 per month. Within one year they went to 149.00. Our property management company want us to go up 10 to 15 percent. We still have 9 units not sold and I am afraid we wont sell any more units if we raise our rates that high. Is that out of line or should I raise the rates that high?