Two Questions health and treadmill

I was recently diagnosed with heart problems, aortic valve stenosis moderate and pulmonary hypertension high side of moderate. I am a 55yr old woman who decided to try exercising more to increase my life span.

I started out January 1 exercising on a Tony Little Gazelle with no results in 14 weeks! I gave it away. I showed no improvement in any area of my health or fitness level and never lost one pound or one inch.

I bought a used older model Precor treadmill. 9.2s to be exact. I am walking at 2.8 on a mostly incline setting for one mile. Is that a good place to start? I was on a 2.3 setting and it took me just about 30 minutes to walk the mile. I want to work out for 30 minutes to start but today of course when I sped up the treadmill I finished in 20 minutes. I went 3.0 for 15-16 minutes but slowed down the last 4-5 to 2.8 and think that is where I need to be.

So my question is, is it better for me to walk a mile faster for a shorter time or slow down and walk the mile in a longer time?

Second is the treadmill question... with my heart problems I will never be able to run but other family members can use the treadmill also so onto the treadmill question.

I told you I bought an older used Precor 9.2s that has always been well maintained. I paid $150 for it after calling around to see what I could expect to pay. I also have the chance to buy a much newer 2006 Vision Fitness Platform T9700s for $500.

My sister will buy the Precor from me if I should be buying the other. I just want to get the most bang for my buck.

Sorry this is so long and thanks for any advice you can offer.

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