Before I wanted to try want to sense if there are concerns breaking the existing install setup by adding binaries with opkg. Now when I did give a try - If it didn't break the install it didn't at least manage to install dig properly.
root@Teltonika-RUT240:~# opkg update
Downloading http://downloads.openwrt.org/chaos_calmer/15.05.1/ar71xx/generic/packages/base/Packages.gz.
Updated list of available packages in /var/opkg-lists/chaos_calmer_base.
Downloading http://downloads.openwrt.org/chaos_calmer/15.05.1/ar71xx/generic/packages/packages/Packages.gz.
Updated list of available packages in /var/opkg-lists/chaos_calmer_packages.
Downloading http://downloads.openwrt.org/chaos_calmer/15.05.1/ar71xx/generic/packages/luci/Packages.gz.
Updated list of available packages in /var/opkg-lists/chaos_calmer_luci.
root@Teltonika-RUT240:~# opkg install bind-dig
Installing bind-dig (9.9.8-P3-1) to root...
Downloading http://downloads.openwrt.org/chaos_calmer/15.05.1/ar71xx/generic/packages/packages/bind-dig_9.9.8-P3-1_ar71xx.ipk.
Configuring bind-dig.
root@Teltonika-RUT240:~# dig --help
dig: can't load library 'liblwres.so.91'
root@Teltonika-RUT240:/usr/bin# ldd ./dig
liblwres.so.91 => not found
libdns.so.169 => not found
libbind9.so.90 => /usr/lib/libbind9.so.90 (0x77414000)
libisccfg.so.90 => /usr/lib/libisccfg.so.90 (0x773f1000)
libisccc.so.90 => /usr/lib/libisccc.so.90 (0x773dc000)
libisc.so.106 => not found
libcrypto.so.1.0.0 => /usr/lib/libcrypto.so.1.0.0 (0x7727e000)
libdl.so.0 => /lib/libdl.so.0 (0x7726a000)
libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x77246000)
libc.so.0 => /lib/libc.so.0 (0x771d9000)
libdns.so.100 => /usr/lib/libdns.so.100 (0x7709a000)
libisc.so.95 => /usr/lib/libisc.so.95 (0x7704f000)
ld-uClibc.so.0 => /lib/ld-uClibc.so.0 (0x7742e000)
root@Teltonika-RUT240:/usr/lib# ls -la liblwres.so*
lrwxrwxrwx 1 root root 18 Nov 15 14:24 liblwres.so -> liblwres.so.90.0.7
lrwxrwxrwx 1 root root 18 Nov 15 14:24 liblwres.so.90 -> liblwres.so.90.0.7
-rw-r--r-- 1 root root 47352 Nov 15 14:11 liblwres.so.90.0.7
root@Teltonika-RUT240:/usr/lib# ls -la libdns.so*
lrwxrwxrwx 1 root root 17 Nov 15 14:24 libdns.so -> libdns.so.100.2.2
lrwxrwxrwx 1 root root 17 Nov 15 14:24 libdns.so.100 -> libdns.so.100.2.2
-rw-r--r-- 1 root root 1238680 Nov 15 14:11 libdns.so.100.2.2
root@Teltonika-RUT240:/usr/lib# ls -la libisc.so*
lrwxrwxrwx 1 root root 16 Nov 15 14:24 libisc.so -> libisc.so.95.5.0
lrwxrwxrwx 1 root root 16 Nov 15 14:24 libisc.so.95 -> libisc.so.95.5.0
-rw-r--r-- 1 root root 240764 Nov 15 14:11 libisc.so.95.5.0
Also this posting makes me hesitate opkg install is supported option.
https://community.teltonika-networks.com/1594/any-plans-to-upgrade-to-latest-openwrt-18-06-or-at-least-kernel