You say you have 4000 "pieces of calculation" and i dont know what that means from the context of what youre doing, but it sounds a lot.
Youre running ReadyAPI! on an 8Gig RAM, I5 and 8 used to have q lot of trouble running my tests on an I5 until i bought an I7 about 4 years ago. Im not saying you cant run ReadyAPI! on an I5, but it depends on the contents of your project file.
Have you launched windows taskmanager to check RAM and processor usage when trying to run your tests? It sounds like your resource profile is hitting your hardwares capacity.
Theres a vmoptions file that allows you to tailor your java heap size etc., but it doesnt work magic, bit that might help a little.
There is a Delay step you might add to your tests to slow them down, diminishing the amout of resource needed at any particular time, not a great reason to add a weight in...server latency yes, but client latency?
Anyway....thats all you got im afraid...maybe kill everything elsr running on your laptoo before you try executing your tests.
Its either try the above or change machines!
if this helped answer the post, could you please mark it as 'solved'? Also if you consider whether the title of your post is relevant? Perhaps if the post is solved, it might make sense to update the Subject header field of the post to something more descriptive? This will help people when searching for problems. Ta