If it is a tissue valve, you will likely get another 10-15 years out of it. A lot of it depends on what kind of valve it is.
Do you know whether it is a homograft (human freeze-dried tissue), stented porcine (pig valve with a stent that is used to sew onto), stentless porcine (pig valve with no stent to sew onto) or bovine (valve fashioned out of cow parts).
Each has its own strengths and weaknesses and each tends to have a little different life span.
A lot of it also depends on the age of the patient. For example, a stented porcine valve will not last very long in a very young person, but they do pretty well when used in elderly patients.
Regardless, you can certainly expect another 8-15 years or so from your valve, based on your age and the assumption there are no other complicating medical factors.
Kev