The FormatsToProcess hang is the clue: Import-Module PSReadLine blocks reading a .ps1xml format file, and the "exactly 15 seconds, every time, no CPU" pattern is a blocking I/O timeout. The format files are loaded lazily on first use, which is why the first call is slow and the next call is instant (the file is already in the OS file cache), and why Get-PSDrive and Import-Module PSReadLine "share" the cost — whichever touches the module data first pays the 15s.

What would cause a consistent per-file read timeout:

1. A PSModulePath entry pointing at a network or cloud-synced location (OneDrive, a mapped drive, a synced Documents). PSReadLine's format files end up on a path that isn't really local, and the read stalls until the provider times out. This is the Update readme #1 suspect — especially if $HOME or Documents has been redirected to OneDrive.
2. Antivirus / real-time scanning intercepting reads of the .ps1xml (consistent delay per distinct file read).
3. A stale per-user PSReadLine install in a cloud-synced path that shadows the one in $PSHOME\Modules.

Debug in this order:

# 1. Where do PSReadLine's files actually live?
Get-Module PSReadLine -ListAvailable | Select-Object Path, Version

# 2. Are any PSModulePath entries non-local (network/cloud)?
$env:PSModulePath -split ';'

# 3. Confirm and time the specific read
Measure-Command { Import-Module PSReadLine -Verbose }

If a non-local path shows up in step 2, that's almost certainly it. Fixes, in order of preference:

• Remove the cloud/network path from $env:PSModulePath (set it explicitly in your profile, keeping the system paths).
• Move the PSReadLine module so it resolves from a truly local folder, e.g. $HOME\Documents\PowerShell\Modules not under a OneDrive-redirected folder — or let it load from $PSHOME\Modules (the version bundled with 7.x is fine; the per-user copy is often stale anyway).
• Add an antivirus exclusion for $PSHOME\Modules and your module folder.

Also worth ruling out quickly: a redirected %USERPROFILE%/$HOME (check $HOME, [Environment]::GetFolderPath('UserProfile')). If $HOME itself points into a synced folder, PSReadLine's history/format files go there with it.

If none of that fits, capture it with ProcMon (Sysinternals), filtered to pwsh.exe and the .ps1xml extension — you'll see the exact file and the 15-second gap in the operation's duration. That will pinpoint whether it's a network/cloud provider or AV before you change anything.