15 STR gives 5 PS which is not enough unless you're on a horse or just damned good at melee. 18/18 is far superior and gives tons of points.
Level 30
18/18
IF: 6
PS: 6
Shield: 5
Athletics: 6
WM: 6
1H: 100
Xbow: 133
Can switch the IF for riding and be a solid cav with good ground ability, or if you're not going hybrid like i did drop 3 off WM and put them wherever you want. If you want to go 2her or dedicated polearm drop the points from shield and 3 points from WM and pick up another 3 points in AGI for 1 more Ath or another 3 in STR for 1 more PS.
e: Now that the steel shield is 2 slots there's almost no reason to get shield 6. It's heavy, slows down your swings, and removes a slot that could be used to carry a side pike or longspear on maps where cav is ruining your team.