Matured endowment: repay early or re-invest?

Hiker_Biker

Our 25 year endowment (£30k life insurance but only reached £24k) has just matured but we switched provider and re-mortgaged in 2000 to pay for home improvements and the current mortgage (£50k) has 13 years still to run. More by luck than judgement, we've ended up with an interest rate of only 1.5% :T, so might it be better to leave the endowment invested? (There is a £6,000 shortfall on the original £30,000 interest-free part of the new mortgage, with another £20,000 as normal re-payment.)
Alternatively, should we cash in and re-invest elsewhere? However, unless invested in tax-free savings, e.g. the currently unavailable NS&I Savings Certificates (e.g. one each at £12k), we'll lose out by having to pay interest. But, if these Savings Certificates are re-issued, we might get better growth and be able to either pay off the endowment-linked part of the loan early or let it run until 2025 to end up with excess funds.
The MSE savings calculator shows that we need an interest rate of only 1.8% for £24k to grow to £30k in 13 y, so a higher interest rate would result in a nice lump sum for us to spend! :j
The third alternative, of course, is to pay off £24k of the £30k now; but with the interest rate at only 1.5%, is that such a good idea?