In D&D 3.5, according to page 79 of the PHB under the move silently skill:
You can move up to one-half your normal speed at no penalty. When moving at a speed greater than one-half but less than your full speed, you take a –5 penalty.
And, according to page 76 of the PHB under the hide skill:
You can move up to one-half your normal speed and hide at no penalty. When moving at a speed greater than one half but less than your normal speed, you take a –5 penalty.
I have no special abilities that have any relevance to this circumstance
I am able to move silently and hide in the same round
I wanted to do this without incurring a penalty on my skill checks
My normal movement speed is 30ft
Would my speed, which I have opted to reduce, be to 15ft or would it be 7.5ft?