Use ArcGIS Online basemaps with UTM-cached imagery

[JohnNergeBrooklynPark]

I have a use case where I want to use an ArcGIS Online basemap and some imagery services that I don't own and has been cached in NAD83 (UTM zone 15N). Here's one of the imagery services in question: https://gis.hennepin.us/arcgis/rest/services/Imagery/UTM_Aerial_2024/MapServer

If you view it in ArcGIS JavaScript or the Map Viewer you'll see it's nice and snappy because it's being used as the basemap. However, if you add it as a map layer to a new map in the AGOL Map Viewer, the performance is significantly degraded.

The AGOL basemap and imagery service play perfectly nicely together in Pro, which I know is a lot more powerful than the map viewer, but also this is for a web app so that's not a solution. Any ideas on how to use a web map with an AGOL basemap and a cached map layer that's not in Web Mercator without degrading performance?

[JonM32]

@JohnNergeBrooklynPark I think that's just how it is in the web. I assume the delay is reprojecting it to WGS.

It is weird how when you view it as a basemap in AGOL from the rest URL in your post, it loads fast. But when I opened it in a map and moved it to a layer. Then back to a basemap. Performance got slower.

[JohnNergeBrooklynPark]

Yep that's my understanding, and I've seen using the UTM or other coordinate system basemap as the solution in other posts. But I'm still curious/hopeful there's a configuration that'd make it possible to use both but still have good performance. If not then I may change this over from a question to an idea.