Help please re keeping endowment money

squashabe

Hello, can anyone please help. We have a mortgage and £15,000 is on interest only and we have this money in a savings account. The mortgage deal expires in July this year and the amount we owe is £52,000. We have an opportunity to fix a mortgage for 5 years at 3.89 or 4.09, one has a £499 fee. We are planning on home improvements and we are thinking of keeping the endowment money and putting all the £52000 on repayment over 10 years. Assuming we can keep an interst rate of about 4% over the loan period it appears that for the £52000 loan it will cost approx. £63,000 (original loan +interest)and for the £37,000 loan it will cost £45,000 (original loan+interest). Paying off the £15000 endowment saves us £3000. If I'm correct it will cost us approx. £3,000 to keep the 15000 (approx 3.8%)and use on home improvements. I've worked out that to borrow £15,000 over 10 years at 6% would cost £4,800. It seems to make sense to keep the endowment money, particularly as until we use it it is making interest. Does thai make sense or am I missing something?
Thanks and I look forward to hearing from anyone who can help.

Regards

Adrian