Shifting between package header and package body (either using Ctrl-H or clicking on the tabs) is slow in version 15.
In version 14, it happened almost in an instance, but in version 15 it is more sluggish (like a full second), you can litterally see PLD removing all visual objects and code and then redrawing everything again.
When you have a package with only a header (e.g. for types or constants), the sluggishness stands out when you press Ctrl-H, because here there is nothing to be shifted as I only have one tab page.

Could seem that it has (also) something to do with the icon size. I have chosen the smallest-but-one icon size. If I change it back to largest icons, it performs better.

We'll check it out.

Do you have the Code Contents enabled? Could it be that the Code Contents redrawing is slow? Is it fast when you disable the Code Contents?

If I turn off Show code contents it is still sluggish. Only when I also turn off Hot track code contents, Show code hiararchy, Hot track code hierarchy, it performs good, almost as fast as in version 14

We'll investigate.

We tried to reproduce this with a package body with 31,000 lines (1 MB). Switching between the spec & body takes about 0.1 second, even with the Code Contents and all other features enabled. Can you let me know your package size? If you can send it to me so that we can reproduce, that would be great.

Package with ~4900 lines in body, file size ~380 kb.
Interesting thing, though: if opened from the file system, switching between package header and body is fast, when opened via database (view spec and body), the switch is slow.

Can it be the showing of compiler warnings:
PLW-07206: analysis suggests that the assignment to 'xyz' may be unnecessary
PLW-07207: BULK COLLECT used without the LIMIT clause
etc.
that slows it down (14 warnings in total)?

If I compile the file into the database, it becomes slow again, so maybe it is the showing of the pane with warnings, compiler hints etc. that is slow?

Okay. We'll look into that!

Solved in beta 3