history /r very slow

Jun 5, 2015
I like to restore old history in new sessions using command "History /R %_HLOGFILE" in tcstart.btm.
Recently I have increased history size to to 500k in order to keep a larger history and noticed that history /r is strangely slow.
To read a 500k history file (which contains about 20k lines and e.g. "type %_HLOGFILE" can show in less than 0.1s), "history /r" takes over 20s to load it.
This is using tcc/le x64

Exactly same time.
Note that I've "Copy to end" ON and Duplicates OFF...so there should be no time wasted looking for previous duplicates.
I'm also seeing some unexpected behaviors if I specify a History File in the OPTION dialog, so I'll need to go back to explicitly load/save history from tcstart/tcexit.btm
One side effect of using an History File (entry in OPTION settings) is the following:
1 I'm using global history list
2 I launch first tcc instance
3 tcc reads history from file
4 I type a few commands
5 I launch a second tcc instance
6 second instance reads history file again (bug?, when using a global list this should be skipped in my opinion)
7 by reading the history file again, commands typed at step 4 are lost or shifted to much up in the history

Is there any way, in TCC/LE, to detect (in a btm file) if current tcc instance is the first/only one or there are other running instances? So I can read history from tcstart only for the fist instance.
Alternatively, is there any way to detect if the history is empty?
Given that I'm trying to keep a 500K history, that execstr doesn't seem such a good idea to me. And history /tn is not available in tcc/le.
So let's consider this a bug report both for the crawl-like loading speed of the history from file, and also for the fact that starting a second shell with global history shoudln't reload the history at all (when a History File is specified in History->Command line)....and,btw, when closing a secondary shell shouldn't save the history either....