Torey,
I think the 115 is marginal but will work ok for general cruising and fishing (assuming you aren't planning on pulling heavy skiers, loading the boat too heavily, etc.). I have the 130 on my 2002 19 Tournament and it works just fine (almost 10 years and more than 600 hours largely running in the ocean). It is substantially heavier than your engine. I think your boat weighs in the same range as mine, and I don't know whether the difference in our hulls has any effect. A lot of the 19s from my year had the Honda 130 as the normal alternative choice was the 150 Yamaha hpdi 2 stroke (or even the 200 hpdi).
I have a friend with a 19 from the 1980s that has a 115 Yamaha 2 stroke, and it works fine. The power is marginal but it works for cruising around and fishing.
I agree with the others that 70 hp likely will be unsatisfactory.
Being as you have the 115, I would put it on and try it out as I think you will be ok with it. Expect a cruise of 18-22 mph and a top speed near 30. If you decide it is not enough power after living with it for a while, you can look for a 150 hpdi.
Frank