At the temps you're talking about- you're going to get a thin bodied beer like a Pilsner or pale ale.
There is a huge difference between 150, 152, 154, 156, and 158 mash temps. The most noticeable will be the body of the beer. The second will be efficiency. I've been to way too many breweries where their stouts have the same body as their pale ales. The reason is they "set it and forget it" and the mash temp drops over the course of the mash.
You'll never really get a great porter or stout unless you can hold the mash temp +\- 1 degree.
If this is a problem- you're better off starting on the high side and dropping into your target temp than you are trying to raise the temp to target.
Higher temps conversion rates are quicker but less efficient. If you're temps drops below the body style you're shooting for you'll also get higher alcohol but a drier beer.
For medium bodied or rich bodied beers raising the temp to mash out is critical to "lock in" the conversion versus continuing conversion during mash out as the temp drops- reducing body, increasing ABV, reducing residual sweetness.
This doesn't match my experience very well at all. There is a huge difference between 147F and 162F mash temps, but I haven't seen a significant difference in my end results with mash temps ranging between 150F and 155F or so. Lagunitas mashes their IPA at 160F, but it doesn't have a body like a stout. Malt today is so hot with enzymatic content that mash temperature just doesn't have a huge effect unless you're at relative extremes in the range.
I completely disagree that you need to be able to hold your mash temp to within a degree to produce a good porter or stout. Most homebrewers don't have that capability, but still produce excellent full-bodied beers. Like any beer, you may have to adapt a recipe to fit your system in order to really dial it in. But the ability to do so is well within the reach of a knowledgeable homebrewer.