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@Washiku, the most important factor IMHO will be your type of car, the use of car, and the roads used for driving your car.

1. Size 17 low profile tyres are expensive to maintain on regular Kenyan roads, they develop dumps on the sides too often even before they wear out. You must be one very careful driver to see the tyres through their normal life cycle. Potholes and stones in gravel roads also tend to bend the rims on such low profiles as size 17 and above.
2. The cost of replacement of these tyres is very high.
3. Stability is not affected by either normal size or low profile as long as the wheel diameter remains unchanged.

Final word: The depth of your pockets and nature of terrain used vis a vis whether car is SUV or sedan type.

Not necessary if you shift to bigger aspect ratio tires to account for the difference in rim size. As long as the overall wheel diameter remains the same you should leave the speedometer and mileage counter alone. Otherwise you ought to have the car computer reconfigured accordingly. Changing overall wheel diameter by more than 2 inches is strongly discouraged though since it's likely to adversely affect the car's geometry. Not to say I am an engineer though.

reduced by 5.3%

Tire math is fairly straightforward. What complicates it is the fact that all the numbers are expressed in different units. The width is expressed in millimeters, the cross-sectional
height as a ratio and the rim radius in inches. You can always work out the overall tire diameter with these values though.