How can I calculate the yield strength of steel tube?
Some physics.  Assuming the same material, length and loading, the bending strength is limited by the Second Moment of Inertia (I) of the cross sectional area.  The math is complex, and even given a calculator, it's a bit confusing.  

Assuming a vertical loading, You can estimate the relative change in the I value by cubing the scale change. (This estimate is accurate only for solid rectangular beams)  This suggests that multiplying the vertical dimension by 1.5 would give a resulting increase in strength of 3.375 times.  

If you're increasing the horizontal thickness, then you simply multiply by the scale.  So increasing thickness by 1.5 would result in a strength increase of 1.5

I ran some numbers in an I calculator, and assuming a 3mm thickness, I got a value 3 times higher for 1.5" than for 1" if loaded against the longer axis, which shows that the estimator is reasonable.  

For a 3mm tube of one inch, I got values of .8 and 2.75 for 1.5".  

All things being equal, a hollow square is better than a hollow circle, and a hollow rectangle is better than both -- if you load it in the right direction.