Indonesia is clearly the larger of the two: about 1,872,242 km² km² against 1,296,279 km² km², roughly 1.4× at true size. Drag one onto the other on the map above to feel the gap.
Indonesia sits in Asia, Peru in South America. On the old Mercator map the latitude gap distorted how large each felt beside the other; at true size the answer is simply 1.4×.
The old Mercator map treated both about equally (1× vs 1× inflation), so at least their relative sizes were preserved — even if both were drawn at the wrong absolute scale.
Peru fits 1× into Indonesia.