Btw., there is a workaround for 15-number limit. A cumbersome one, but when someone needs to make exact mathematical calculations with such numbers, then:
1. Divide the number to 2 parts and enter them in separate cells (columns). (you can also enter the long number as text, and use formulas to divide it.)
P.e. to make calculations with integers like 123456789012345678 enter it as 123456789 and 12345678, or to make calculations with decimals like 0.123456789012345678 enter it as 0,123456789 and 12345678 (or 0.012345678);
2. Design formulas (or user-defined functions) for mathematical operations with such number pairs. NB! You need 2 formulas for one operation. And when you write a function, then it must have a parameter, determining which part of result is returned. You can then use formula to get result returned as long number in text format too.