your plant looks quite yellow (but maybe it's from the lighting in the pic?), so perhaps the reason it is growing so slowly is because it needs food!

transplanting is a good idea tho. whenever i have transplanted my plants they have just exploded in growth!! a lot of people say that when u transplant your plant may not grow too fast until it recovers from the shock, but that hasnt been my experience at all. mine grow like an inch overnight, after being transplanted.