Custom Designer Brush Lag

[pai]

Hi,

Now, I have created few brushes from AR5 brush designer tool. I only use 2048x2048 preset default basic canvas to test these strokes. I found out whenever I blend colors or even just continuously few strokes, it lags a lot and have that loading % bar running frequently. Like I have to pause every stroke I put down on canvas now. Even I zoom in like 300%, it's the same

Am I missing something to be able to run these custom brushes more smoothly?

Using Windows 7
i7-3770, 32MB Ram