5.* series builds defective on Slackware

Hi all,

Building from 5.1.0.* sources on 64-bit 
Slackware (14.1 and 14.2 beta) produces a build 
defective in a very important aspect -- such 
build opens the fairly big document overly slow.

Things go like this: unpacking stage passes 
quick (judging by the status bar), then UI 
updates stop, and only after quite a longish 
time (~10 secs with the sample doc) the doc 
content is displayed.

The 4.3.7.2, built in the same environment, 
shows no such problem, displays content like 
after 1-2 secs after unpacking complete.

The binary 5.1.0.* downloaded from pre-releases, 
shows no such problem, metrics about the same.

A sample doc of sufficient size to make the 
issue noticeable is at:
https://bugs.documentfoundation.org/attachment.cgi?id=121623

I build with:

./configure \
--with-external-tar=$HOME/c/libo/ext5 \
\
--with-krb5=no \
--with-gssapi=no \
\
--disable-gstreamer-1-0 \
--disable-gstreamer-0-10 \
\
--without-fonts \
--without-junit \
--with-system-libs=no \

I don't know anything about linux profiling 
and/or debugging. Could somebody help? Should I 
build in some other distro (in emulator)? 
Building 4.* series was okay.
-Yury