Size and weight are big decision factors when you are trying to find the ideal camera for your needs.
In this section, we are going to illustrate the Olympus SZ-15 and Pentax Q-S1 side-by-side from the front, back and top in their relative dimensions. Olympus SZ-15 has external dimensions of and weighs 250 g (0.55 lb / 8.82 oz) (including batteries). Pentax Q-S1 has external dimensions of 105 x 58 x 34 mm (4.13 x 2.28 x 1.34″) and weighs 203 g (0.45 lb / 7.16 oz) (including batteries).
Below you can see the front-view size comparison of the Olympus SZ-15 and the Pentax Q-S1. Pentax Q-S1 is clearly the smaller of the two cameras. Its body is 3mm narrower, 12mm shorter and 6mm thinner than Olympus SZ-15. As you can tell, actually this is not a fair size comparison since Olympus SZ-15 has a built-in lens but Pentax Q-S1 doesn't. Once you put a lens on Q-S1, its thickness will increase significantly.
Here is the back view size comparison of the Olympus SZ-15 and Pentax Q-S1.
Now lets look at the top view comparison of Olympus SZ-15 and Pentax Q-S1.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Pentax Q-S1 is significantly lighter (47g ) than the Olympus SZ-15 which may become a big advantage especially on long walking trips.
Again, this comparison may not be very useful in real life as we are comparing the weight of a camera with a built-in lens to the body-only weight of an interchangeable lens camera. Once you put a lens on Q-S1, the total kit will weigh much higher.
Weather Sealing
Unfortunately neither the Olympus SZ-15 nor Pentax Q-S1 provides any type of weather sealing in their bodies, so you have to give extra care especially when you are shooting outdoors. If weather sealing is a must-have feature for you, check these sections: Top Compact Cameras with Weather Sealing Top Mirrorless Cameras with Weather Sealing
LCD Screen Size and Features
Olympus SZ-15 and Pentax Q-S1's LCD screens have the same diagonal size of 3.00 inches.
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.