Opera Mini vs Other Browsers

Haven't experienced the difference you're citing. I suspect, however, that Opera may be somewhat smaller than the other browsers and depending on the other apps you have that are actually running at the same time, the browser may lag if the o/s is working to meet the demands of the various apps. With a smaller browser, the problem may not crop up.

If that's true, there's little you can do about it other than not to put such heavy demands on your o/s. (And you may not realize you're doing so.) It's the price one pays for an o/s like Android that allows virtually unlimited multitasking with third party applications.