L1, L2 is two levels of cashe memory in computer .

A CPU cache is a cache used by the central processing unit of a computer to reduce the average time to access memory. The cache is a smaller, faster memory which stores copies of the data from the most frequently used main memory locations. 

using two level cashe memory – may be more than two – save time compared to
having to get it from random access memory .

L1 : is that first level inside the microprocessor chip very fast in processing .

L2 : is separated in outer chip less speed than L1 but still faster  than RAM  .

so increasing  cashe levels will increase  processing speed and so our pc performace .

Why not just have a big L1 cache? The L1 cache is extremely expensive.
So the L1/L2/L3 system makes for great (not optimal, if you had a
really big L1 cache it’d be faster) performance that doesn’t cost an
arm and a leg.