(better late than never)
One can use blastn with
-task blast-short, and it's quite fast. As explained in the manual (section BLAST+ features), "blastn-short is BLASTN program optimized for sequences shorter than 50 bases". Further down (table C2), it says "blastn-short is optimized for sequences less than 30 nucleotides" and specifies word_size=7 (versus 11 for blastn) and reward=1 (versus 2 for blastn), all the other parameters remaining as for blastn.
In a Unix-like machine, with NCBI BLAST 2.2.26+:
zcat genome.fa.gz | formatdb -i stdin -l formatdb.log -p F -n genome
blastn -query primers.fa -db genome -task blastn-short -out primers_one_genome.txt -outfmt 7
If one knows both primers around the sequence they amplify, I recommend concatenating them into a single sequence, and map it to the genome. BLASTn-short will usually (likely?) return two best hits, one per primer, separated by a gap on the genome.