15,520px × 7,760px ≅ 120 MP
@boris Please update How can I upload imagery to Mapillary? – Mapillary to reflect the true resolution limit. Insta360 X Series – Mapillary may need some updates too. 
While at it, I wish MapillaryJS would also finally solve [🐛] Zoom‑in limited by maximum texture size and Why does the view get blurry on Mapillary at higher zoom levels?, although I do understand that it adds complexity to rendering code. But, this code path would only run in canvases where GL_MAX_TEXTURE_SIZE is smaller than any image dimension. Afaict the overall performance impact should remain negligible. Watch out for (silent) GL_OUT_OF_MEMORY though!