Swaziland is about 15 times smaller than New Zealand.

New Zealand is approximately 268,838 sq km, while Swaziland is approximately 17,364 sq km, making Swaziland 6.46% the size of New Zealand. Meanwhile, the population of New Zealand is ~5.1 million people (3.9 million fewer people live in Swaziland).
Tip: This to-scale comparison of New Zealand vs. Swaziland uses the Mercator projection, which distorts the size of regions near the poles.