I sold my EPS a long time ago so I don't remember where, but there should be a soft page that list the details of your EPS including how much memory you have installed. However, with 4megs, a stereo sample at 48 KHz should yeild about 20 seconds of sample time. Since you sataed that you are getting around 19 seconds, and if that is in stereo, you may already be at the 4meg max.
I didn't think of this earlier but in addition to lowering the sample rate, you can almost double your sample time by sampling in mono rather than stereo.
Sampling things with high frequency content (cymbals, woodwinds, etc.) should be sampled at higher rates but do not necessarily need to be sampled in stereo. Bases, on ther other hand usually don't contain high frequencies and can be sampled at a slightly lower rate. So, by keeping the frequencies of what you are sampling in mind, as well as the need for a stereo image, will help you to conserve memory.
In my opinion, the memory limit was the only drawback of the EPS, otherwise it's a great sampler with killer effects.