Generate the feasible list of combinations

Question

I have used the following function to generate fund combinations in a portfolio. For example, I have four funds in the portfolio. The incremental change of each fund is 5. The range of allocations for each fund is between 0 and 100.

import itertools
from collections import Counter

def sums(n,r):
    solutions = []
    c = {k: v for k, v in zip(range(r), [0]* r)}
    for tpl in itertools.combinations_with_replacement(range(r), n-1):
        d = c.copy()
        d.update(Counter(tpl))
        solutions.append(tuple(map(lambda x: x*INCR, d.values()) ))
    return solutions

funds = 4
INCR = 5

Comb = [t for t in sums(int(100//INCR), funds) if min(t) >= 0]

len(Comb)

It works fine until the number of funds get larger. It takes forever to get results for 15 funds because the number of combinations become huge. For a portfolio of 15 funds, I actually have range limitations for each fund. For example, the range for the first 10 is between 0 and 25. The range for the last 5 is between 0 and 10.

How can I apply the range of each fund into the function to avoid generating the huge number of total combinations? Thanks for any inputs.