Bicep Curling with more Weight than French Preses

So, I have been doing the W4SB program for over a month now with the main goals of gaining muscular size and strength. On the repetition upper body days I have been doing the standing dumbbell French press exercise -with one dumbbell in each hand- for primarily the triceps and the standing alternating dumbbell bicep curl as my elbow flexor exercise.

The thing is is that it seems that I can only French press with 15 lbs. in each hand for about 10 reps at the most (without going to failure) while I can do standing alternating bicep curls with 20lbs. in each hand. for about 10 reps on each arm (without going to failure). I know that the triceps are supposed to be stronger than the biceps. So I am wondering if I actually have muscular imbalances in my upper arms?